Currently, in the photographic industry, microdots are placed on professional-grade photographic paper for identifying the image captured thereon as copyrighted. U.S. patent application Ser. No. 08/598,778 discloses such copyrighted images having microdots. The microdots are typically yellow in color before an image is printed on the document, and after an image is printed thereon, the color of each microdot is a combination of the original yellow color and the particular color of the image at the location of the microdot.
Under normal viewing conditions the microdots in the document are invisible to the unaided human eye. However, when a digital image of the document is made by a digital copying apparatus, the presence of the microdots can be detected by means of presently known image processing for indicating to the user that the image is copyrighted and should not be reproduced without the photographer's authorization. Upon this detection, the copying apparatus is precluded from making a copy.
In some situations, however, there is a legitimate reason to make a copy of the copyrighted document, and it becomes necessary to remove the microdots from the digital image of the documents. This is especially true if the image is enlarged so that the microdots become readily visible to the human eye.
The current solution to this problem is to use a "dust and scratch" removal algorithm that is commercially available.
Although the presently known and utilized method for removing microdots is satisfactory, it is not without drawbacks. While the above-described method will remove most or all of the microdots from the digital image, it will also slightly degrade a portion of or the whole image.
Consequently, a need exists for overcoming the above-described drawback.